Acute poisoning and suspected overdose

Acute poisoning is harm from a substance taken, injected, inhaled or absorbed, by accident, intentional self harm, recreational use, therapeutic error or malicious intent. The care sequence is to stabilise airway, breathing and circulation, treat life threats and give antidotes early, limit absorption when it is useful, identify the agent, and assess risk of self harm.

Epidemiology. Self poisoning is common in young adults, and children usually take single accidental ingestions. Paracetamol, opioids, benzodiazepines, antidepressants, alcohol, pesticides, household products and plant material cause most presentations, and the local pattern varies (organophosphate pesticides, paraquat and plant poisons are major causes in many rural settings).

Toxidromes.

Severity. Dose, time since ingestion, co-ingestants, age, comorbidity and delayed toxicity (modified release products, paracetamol, iron, toxic alcohols, antifreeze, colchicine, sulphonylureas, amatoxin mushrooms) matter more than the initial look of the patient.

Key distinctions. Early good condition does not exclude serious delayed toxicity. A mixed ingestion is the rule in self harm. Toxicology screens are slow, miss many agents and do not direct emergency treatment.

History (from patient, family, ambulance staff, packages and pharmacy). Agent, formulation (immediate or modified release), dose, time, route, co-ingestants and alcohol, symptoms, vomiting, intent (including suicidal thoughts and plans), prior attempts, psychiatric history, medicines available at home, and access to others' medicines. Ask about the household for children (all medicines, button batteries, magnets, plants, cleaning products).

Examination.

• Airway and breathing, pulse, blood pressure, temperature, respiratory rate, saturation, glucose, Glasgow Coma Scale, pupils.
• Skin (sweating, dryness, flushing, needle marks, bullae, jaundice), mouth (burns, salivation), breath odour (alcohol, ketones, garlic from organophosphates and arsenic, bitter almonds from cyanide), muscle tone, clonus, tremor, reflexes, bowel sounds, bladder.
• Cardiovascular rhythm and QRS and QTc intervals.

Red flags.

• Glasgow Coma Scale 8 or less, respiratory rate under 8 breaths/min, saturation under 92%, seizures.
• Systolic pressure under 90 mmHg, QRS over 100 ms, QTc over 500 ms, ventricular arrhythmia.
• Temperature over 39 °C, metabolic acidosis (pH under 7.3), potassium over 6.0 mmol/L.
• Ingestion of agents with delayed toxicity, deliberate large ingestion, or suicidal intent.
• Children: ingestion of any single tablet of sulphonylureas, calcium channel blockers, opioids, tricyclics, camphor or chloroquine can be fatal.

Special groups. Children (weight based dosing, accidental ingestion, consider non-accidental), pregnancy (treat the mother first, and discuss with obstetric and poison services), older adults (therapeutic errors, polypharmacy), and patients in drug misuse settings (overdose with mixed agents, naloxone supply).

Poisoning by toxidrome (unknown agent).

• Opioid and sedative: opioid poisoning, benzodiazepine poisoning, barbiturate poisoning, gamma-hydroxybutyrate poisoning, alcohol intoxication, clonidine poisoning.
• Anticholinergic and sympathomimetic: tricyclic antidepressant poisoning, antihistamine poisoning, antipsychotic poisoning, cocaine toxicity, amphetamine toxicity, theophylline toxicity.
• Cholinergic: organophosphate poisoning, carbamate poisoning, nicotine poisoning, mushroom poisoning.
• Cardiovascular drugs: beta blocker poisoning, calcium channel blocker poisoning, digoxin toxicity.
• Metabolic and delayed: paracetamol poisoning, salicylate poisoning, iron poisoning, methanol poisoning, ethylene glycol poisoning, isopropanol poisoning, metformin associated lactic acidosis, sulphonylurea poisoning, insulin overdose, lithium toxicity, colchicine poisoning, paraquat poisoning, amatoxin mushroom poisoning.
• Gases and asphyxiants: carbon monoxide poisoning, cyanide poisoning, hydrogen sulphide poisoning, methaemoglobinaemia.
• Caustics and hydrocarbons: acid ingestion, alkali ingestion, hydrocarbon aspiration, button battery ingestion.
• Anticoagulant rodenticide poisoning, serotonin syndrome, neuroleptic malignant syndrome, alcohol withdrawal.

Mimics (non-toxic causes of the same presentation). Hypoglycaemia, head injury, stroke, subarachnoid haemorrhage, meningitis, encephalitis, sepsis, status epilepticus, non-convulsive status epilepticus, diabetic ketoacidosis, hepatic encephalopathy, hypothermia, thyroid storm, cardiac arrhythmia, psychiatric illness.

Immediate. Capillary glucose, 12 lead ECG (QRS, QTc, rhythm), continuous monitoring, blood gas with lactate, electrolytes (anion gap), urea, creatinine, liver tests, full blood count, coagulation, creatine kinase, paracetamol and salicylate levels in every intentional or unknown overdose, and a pregnancy test in women.

Interpretation.

• Anion gap = sodium minus (chloride plus bicarbonate); over 16 mmol/L is raised. Osmolar gap over 10 mOsm/kg suggests toxic alcohols (it may be normal late).
• Paracetamol:
  • Take the 4 hour level (not earlier).
  • Treat at or over the 100 mg/L line at 4 hours (150 mg/L is used in some practice), repeating at 8 hours if unclear.
  • Treat without waiting for a level when the time is unknown, when ingestion is staggered over more than 1 hour, when the amount is over 75 mg/kg (or over 12 g), or when ALT is raised or paracetamol is detectable at over 8 hours.
• Salicylate: repeat levels every 2 to 4 hours, since absorption continues and levels may rise; a level over 300 mg/L suggests significant toxicity.
• Drug levels where relevant: lithium (12 hours after the last dose), digoxin (6 hours or more after the dose), phenytoin, valproate, carbamazepine, theophylline, iron (4 to 6 hours), and carboxyhaemoglobin.
• Urine toxicology is of limited value and does not change emergency treatment.

Further tests. Repeat ECG at 4 to 6 hours for QT prolonging or cardiotoxic drugs, serial liver tests and INR for paracetamol, serial gases for salicylate and toxic alcohols. Chest radiograph for aspiration, CT head for coma without clear cause, and endoscopy for corrosive ingestion with drooling, stridor, vomiting or chest pain (within 12 to 24 hours).

Limitations. Early paracetamol levels (under 4 hours) are unreliable. Modified release products cause late toxicity and delayed peaks. A normal ECG at presentation does not exclude later conduction defects, and a normal osmolar gap does not exclude late toxic alcohol poisoning.

General care.

• Airway, breathing and circulation first, with oxygen, IV access, and monitoring. Intubate for loss of airway protection or respiratory failure.
• Correct glucose under 4.0 mmol/L (glucose 10% 150 to 200 mL IV over 15 minutes).
• Give thiamine 500 mg IV over 30 minutes before or with glucose in alcohol misuse or malnutrition.
• Treat seizures with lorazepam 4 mg IV (repeat once after 10 minutes; reduce in frail patients) or diazepam 10 mg IV.
• Treat hypotension with isotonic saline 500 mL boluses, agitation with diazepam 5 to 10 mg IV titrated to effect (monitor respiration), and hyperthermia with cooling. Avoid physical restraint where possible.
• Do not induce vomiting. Do not use gastric lavage routinely.

Decontamination.

• Activated charcoal 50 g orally or by nasogastric tube (children 1 g/kg, maximum 50 g), once, within 1 hour of a potentially toxic ingestion in a patient with a protected airway.
• Contraindicated with reduced consciousness without a protected airway, corrosives, hydrocarbons, alcohols, metals (iron, lithium) and ileus.
• Monitor for vomiting and aspiration.
• Repeated charcoal (50 g, then 25 to 50 g every 4 hours) for carbamazepine, dapsone, phenobarbital, quinine and theophylline, with airway protection and bowel sounds checked.
• Whole bowel irrigation (polyethylene glycol 1.5 to 2 L/hour by nasogastric tube until the effluent is clear) for large ingestions of iron, lithium or modified release products and body packers, with a protected airway; avoid in ileus, obstruction or haemodynamic instability.
• Remove contaminated clothing and wash skin and eyes for dermal or ocular exposure, with protection of staff.

Antidotes and specific treatment.

• Opioids:
  • Ventilate first, then naloxone 0.4 mg IV, repeated every 2 to 3 minutes.
  • In chronic users use 0.04 to 0.1 mg increments.
  • Titrate to respiratory rate over 10 breaths/min.
  • Maximum about 10 mg before the diagnosis is reconsidered.
  • The effect lasts 20 to 90 minutes, shorter than most opioids.
  • Consider an infusion of two thirds of the reversal dose each hour.
  • Observe for at least 2 hours after the last dose (up to 6 hours for methadone and modified release products).
• Paracetamol:
  • Acetylcysteine 150 mg/kg IV in 200 mL glucose 5% over 1 hour, then 50 mg/kg in 500 mL over 4 hours, then 100 mg/kg in 1000 mL over 16 hours (maximum weight 110 kg).
  • Monitor liver tests, INR, creatinine and anaphylactoid reactions (pause the infusion, give an antihistamine, restart when settled).
  • Continue beyond 21 hours if ALT is rising, INR is raised or paracetamol is still detectable.
  • Reduce fluid volumes in children and fluid overload.
  • Transfer to a liver unit when INR is over 2.0 at 24 hours, over 3.0 at 48 hours, or encephalopathy, acidosis (pH under 7.30) or creatinine rises.
• Tricyclic antidepressants and sodium channel blockers (QRS over 100 ms, ventricular arrhythmia, seizures or hypotension):
  • Sodium bicarbonate 8.4% 50 to 100 mmol IV (about 1 to 2 mmol/kg) over 5 to 10 minutes, repeated until QRS narrows, aiming for blood pH 7.45 to 7.55.
  • Monitor potassium, sodium, ionised calcium and pH.
  • Avoid flumazenil and physostigmine.
  • Use benzodiazepines for seizures.
• Benzodiazepine oversedation (iatrogenic only; avoid in mixed overdose, epilepsy and long term use): flumazenil 0.2 mg IV over 15 seconds, then 0.1 mg every 60 seconds; maximum 1 mg in one course; monitor for resedation and seizures.
• Salicylate:
  • Sodium bicarbonate 8.4% 1.5 mL/kg IV over 1 hour (or 225 mL in 1 L glucose 5%), then infuse to keep urine pH 7.5 to 8.5.
  • Replace potassium to over 4.0 mmol/L.
  • Avoid acetazolamide.
  • Give oxygen and avoid sedatives.
  • Maintain ventilation (intubated patients need a high minute volume).
  • Haemodialysis for a level over 700 mg/L (5.1 mmol/L), or at any level with altered mental state, pulmonary oedema, kidney failure or pH under 7.2.
• Methanol and ethylene glycol:
  • Fomepizole 15 mg/kg IV over 30 minutes, then 10 mg/kg every 12 hours for 4 doses, then 15 mg/kg every 12 hours until the level is under 200 mg/L (every 4 hours during dialysis).
  • Monitor creatinine, gas and levels; adjust dosing in dialysis.
  • If fomepizole is unavailable use ethanol under specialist direction.
  • Haemodialysis for acidosis (pH under 7.30), visual signs, kidney failure or a level over 500 mg/L.
  • Methanol: folinic acid 1 mg/kg IV (maximum 50 mg) every 6 hours.
  • Ethylene glycol: pyridoxine 50 mg IV every 6 hours and thiamine 100 mg IV every 6 hours.
• Organophosphates:
  • Atropine 2 mg IV, doubling every 5 minutes until secretions dry, the chest is clear, heart rate is over 80 beats/min and systolic pressure over 80 mmHg, then an infusion of 10 to 20% of the loading dose each hour.
  • Monitor for atropine toxicity (delirium, hyperthermia, ileus).
  • Pralidoxime 30 mg/kg IV over 30 minutes then 8 mg/kg/hour (evidence for benefit is limited), reduced in kidney impairment.
  • Use benzodiazepines for seizures and agitation and protect staff.
• Carbon monoxide: 100% oxygen until carboxyhaemoglobin is under 3% (under 10% in smokers) and symptoms resolve; hyperbaric oxygen is considered for loss of consciousness, neurological signs, pregnancy with high levels or ischaemia, but evidence is limited.
• Cyanide: hydroxocobalamin 5 g IV over 15 minutes (children 70 mg/kg, maximum 5 g), repeated once if needed; maximum 10 g; monitor blood pressure and expect red urine.
• Beta blocker poisoning: glucagon 50 micrograms/kg IV bolus (usual 5 mg over 1 to 2 minutes), then an infusion of 1 to 10 mg/hour titrated to heart rate and blood pressure; monitor for vomiting (protect the airway), glucose and potassium. Add high dose insulin and adrenaline or noradrenaline infusions in refractory shock with toxicology direction.
• Calcium channel blocker poisoning:
  • Calcium chloride 10% 10 to 20 mL IV over 10 minutes (or calcium gluconate 10% 30 to 60 mL), repeated every 10 to 20 minutes or by infusion, to a maximum of about 60 mL of 10% calcium chloride.
  • High dose insulin euglycaemia therapy: soluble insulin 1 unit/kg IV bolus, then 0.5 to 1 unit/kg/hour (up to 10 units/kg/hour in specialist units), with glucose 10% to keep glucose over 5 mmol/L and potassium monitoring hourly.
  • Noradrenaline for vasoplegia.
  • Atropine for bradycardia.
  • Extracorporeal support in refractory shock.
• Digoxin toxicity: antibody fragments dosed from the product label by amount ingested or serum level (acute large ingestion needs 10 to 20 vials; chronic toxicity 2 to 5 vials), with correction of potassium and magnesium; avoid calcium salts unless immediately life threatening hyperkalaemia.
• Iron: serum iron over 500 micrograms/dL (90 micromol/L) or symptoms, or ingestion over 60 mg/kg elemental iron:
  • Deferoxamine 15 mg/kg/hour IV, maximum 6 g in 24 hours.
  • Monitor blood pressure (hypotension), allergic reactions and urine colour (vin rose).
  • Continue until the urine returns to normal and the patient is well.
  • Whole bowel irrigation for radio-opaque tablets.
• Sulphonylureas: glucose 10% 150 to 200 mL IV, then octreotide 50 micrograms subcutaneously every 6 hours (or 25 micrograms/hour IV infusion), monitoring glucose hourly for at least 24 hours.
• Insulin: glucose infusion with frequent glucose checks and potassium replacement for the duration of the insulin effect.
• Lithium: isotonic saline to restore euvolaemia and urine output over 1 mL/kg/hour; haemodialysis for neurological impairment, seizures, life threatening arrhythmia, or a level over 4.0 mmol/L with kidney impairment, or consider dialysis for levels over 5.0 mmol/L.
• Methaemoglobinaemia (level over 30%, or symptomatic with hypoxia): methylthioninium chloride 1 to 2 mg/kg IV over 5 minutes, repeat once after 30 to 60 minutes if needed; maximum 7 mg/kg; avoid in G6PD deficiency and with serotonergic drugs; monitor co-oximetry.
• Local anaesthetic toxicity: lipid emulsion 20% 1.5 mL/kg IV over 1 minute, then 15 mL/kg/hour; repeat the bolus up to twice at 5 minute intervals; maximum 12 mL/kg.
• Anticoagulant rodenticide (long acting): vitamin K 10 mg IV (children 250 to 300 micrograms/kg) daily or until INR normalises; monitor INR for several weeks; add prothrombin complex concentrate 25 to 50 units/kg IV for serious bleeding.
• Serotonin syndrome and neuroleptic malignant syndrome:
  • Stop the precipitating drugs, give benzodiazepines, fluids and cooling.
  • Cyproheptadine 12 mg orally or by nasogastric tube, then 2 mg every 2 hours while symptoms continue, then 8 mg every 6 hours; maximum 32 mg daily.
  • Temperature over 41 °C needs paralysis and ventilation.
• Sympathomimetic toxicity: benzodiazepines (diazepam 5 to 10 mg IV, repeated every 5 to 10 minutes), cooling, and fluids; avoid beta blockers in cocaine toxicity; glyceryl trinitrate or phentolamine for severe hypertension or coronary spasm.
• Corrosive ingestion: protect the airway, no induced vomiting, no neutralisation, early endoscopy, and surgical review for perforation.
• Button battery ingestion (oesophageal): urgent endoscopic removal, with honey 10 mL every 10 minutes (up to 6 doses) or sucralfate 10 mL every 10 minutes in children over 12 months who are awake and alert before removal if it will not delay transfer.
• Paraquat: avoid oxygen unless hypoxic; early poison centre direction.

Risk assessment and psychiatric care. Every patient with intentional overdose needs a risk assessment (suicidal thoughts, plans, previous attempts, protective factors) after medical stabilisation, with observation and referral to mental health services. Do not leave a patient with suicidal intent alone, and check capacity before discharge decisions.

Monitoring. Continuous ECG and saturation, hourly observations, glucose checks, urine output, serial gases and drug levels, repeat ECG for cardiotoxic drugs, and liver tests and INR for hepatotoxic agents.

Referral and escalation. Poison centre or clinical toxicology for all serious or unknown ingestions, critical care for airway, ventilatory or haemodynamic support, nephrology for dialysis, hepatology or a liver unit for paracetamol hepatotoxicity, mental health services for self harm, and social care and safeguarding for children.

Admission criteria.

• Admit for symptomatic patients, abnormal ECG, delayed toxicity agents, antidotes in progress (acetylcysteine, fomepizole), or need for monitoring.
• Admit all intentional overdoses until medically clear and assessed by mental health services.
• Observe at least 6 hours after ingestion of immediate release drugs and 12 hours or more after modified release, tricyclic, calcium channel blocker or beta blocker ingestion.
• Observe at least 24 hours for sulphonylurea ingestion.

Discharge and safety netting. Discharge only after medical recovery, a completed risk assessment, a safety plan, restricted access to means (limit pack sizes, lock medicines), and follow up arranged. Patients and carers are told to return for drowsiness, vomiting, abdominal pain, yellow eyes, confusion, palpitations, seizures or breathing difficulty. Provide naloxone supply and training for opioid users, and prevent access to children in the home.